1. Field of the Invention
The present invention relates to a liquid crystal display device having selection switching elements arranged in units of pixels or scanning lines, and a driving method for the device.
2. Description of the Related Art
Liquid crystal display devices are low-profile, lightweight devices which can be driven on low voltages, and hence are widely used for wristwatches, desk calculators, wordprocessors, personal computers, compact video games, and the like. With the recent, increased demand for pen input electronic notebooks, a demand has arisen for portable terminal devices (PDA).
As a method of driving a liquid crystal display device, a driving method of reversing the polarities within the same frame is available. This driving method includes a signal line reversal method of reversing the polarity in units of signal lines, a horizontal polarity reversal (to be referred to as H reversal hereinafter) method of reversing the polarity in units of scanning lines, and a dot reversal method of reversing the polarity between adjacent pixels. These driving methods can compensate for flicker components (e.g., plane flickers) resulting from polarity reversal. The H inversion driving method has been widely used especially as the demands have arisen for arrangement of signal line drivers on one side with a decrease in cabinet size, and for low-withstand voltage drivers for a decrease in power consumption.
In a large-screen, high-resolution LCD, as the number of signal lines increases, the capacitive component between the common electrode and each signal line becomes large. In addition, the resistive component greatly changes in accordance with the distance from the feeding point because of the sheet resistance of the common electrode. For this reason, when the polarity of the common electrode is reversed, since the time constant of the common electrode varies within the frame as shown in FIG. 1, the voltage value of the common electrode varies (the waveform becomes blunt). Since this phenomenon depends on the signal voltage, when window display is performed, picture degradation known as crosstalk occurs. In order to solve this problem, the sheet resistance of the common electrode may be decreased. However, this method has its own limitations, and cannot provide a satisfactory effect.